US 7170356 B2 Abstract A circuit with variable capacitance includes a capacitance, wherein the capacitance includes a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance. The circuit with variable capacitance further includes a unit for providing the first bias and the second bias. With such a circuit with variable capacitance, it is possible to achieve a more linear and flatter characteristic tuning curve of the circuit with variable capacitance as compared to a conventional circuit with variable capacitance in a simple way.
Claims(28) 1. A circuit with variable capacitance comprising:
a capacitance, wherein the capacitance includes a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first bias is defined by a potential difference between the first tap point and a ground potential terminal, and the second bias is defined by a potential difference between the second tap point and the ground potential terminal, wherein the first tap point is electrically connected to a supply voltage terminal of the circuit with variable capacitance, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point; and
a biasing unit configured to provide the first bias and the second bias, wherein the first bias differs from the second bias.
2. The circuit with variable capacitance according to
3. The circuit with variable capacitance according to
4. The circuit with variable capacitance according to
5. The circuit with variable capacitance according to
6. The circuit with variable capacitance according to
7. The circuit with variable capacitance according to
8. The circuit with variable capacitance according to
9. The circuit with variable capacitance according to
10. The circuit with variable capacitance according to
11. The circuit with variable capacitance according to
12. A method for operating a circuit with variable capacitance, the method comprising:
providing the circuit with variable capacitance, the circuit with variable capacitance including a capacitance, wherein the capacitance comprises a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first bias is defined by a potential difference between the first tap point and a ground potential terminal, and the second bias is defined by a potential difference between the second tap point and the ground potential terminal, wherein the first tap point is electrically connected to a supply voltage terminal of the circuit with variable capacitance, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point;
providing the first bias and the second bias by applying a supply voltage to the supply voltage terminal; and
tapping off a voltage dropping at the capacitance of the circuit with variable capacitance to output the same as output signal of the circuit with variable capacitance.
13. A computer readable medium containing program code operable to, when run on a computer, perform a method for operating a circuit with variable capacitance, wherein the circuit with variable capacitance includes a capacitance, wherein the capacitance comprises a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first bias is defined by a potential difference between the first tap point and a ground potential terminal, and the second bias is defined by a potential difference between the second tap point and the ground potential terminal, wherein the first tap point is electrically connected to a supply voltage terminal of the circuit with variable capacitance, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point, the method comprising:
providing the first bias and the second bias by applying a supply voltage to the supply voltage terminal; and
tapping off a voltage dropping at the capacitance of the circuit with variable capacitance to output the same as output signal of the circuit with variable capacitance.
14. An oscillator circuit comprising:
an inductance;
a capacitance connectable in series to the inductance, wherein the capacitance includes a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first tap point is electrically connected to a supply voltage terminal of the oscillator circuit, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point; and
a biasing unit configured to provide the first bias and the second bias.
15. The oscillator circuit according to
16. The oscillator circuit according to
17. The oscillator circuit according to
18. The oscillator circuit according to
19. The oscillator circuit according to
20. The oscillator circuit according to
21. The oscillator circuit according to
22. The oscillator circuit according to
23. The oscillator circuit according to
24. The oscillator circuit according to
25. The oscillator circuit according to
26. The oscillator circuit according to
27. A method for operating an oscillator circuit, the method comprising:
providing the oscillator circuit, wherein the oscillator circuit includes an inductance, a capacitance connectable in series to the inductance, wherein the capacitance comprises a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first tap point is electrically connected to a supply voltage terminal of the oscillator circuit, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point;
providing the first bias and the second bias by applying a supply voltage to the supply voltage terminal; and
tapping off a voltage dropping at the capacitance of the oscillator circuit to output the same as output signal of the oscillator circuit.
28. A computer readable medium containing a computer program with program code, the program code operable to, when run on a computer, perform a method for operating an oscillator circuit, wherein the oscillator circuit includes an inductance, a capacitance connectable in series to the inductance, wherein the capacitance comprises a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, wherein the first partial capacitance includes two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance includes two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first tap point is electrically connected to a supply voltage terminal of the oscillator circuit, wherein the first tap point is connected to the second tap point via a resistor, wherein the resistor connects the second tap point to the supply voltage terminal in a serial connection via the first tap point, the method comprising: providing the first bias and the second bias by applying a supply voltage to the supply voltage terminal; and tapping off a voltage dropping at the capacitance of the oscillator circuit to output the same as output signal of the oscillator circuit.
Description This application claims priority from German Patent Applications No. 10 2004 008 706.7, filed on Feb. 23, 2004, and No. 10 2004 008 701.6, filed on Feb. 23, 2004, which are incorporated herein by reference in their entirety. 1. Field of the Invention The present invention relates to a circuit with variable capacitance and a method for operating a circuit with variable capacitance, and, in particular, the present invention relates to an electronic circuit with variable capacitance whose transition behaviour between a minimum and a maximum saturation value is variable. 2. Description of the Related Art A conventional voltage controlled oscillator (VCO) in most cases has one or more characteristic tuning curves, wherein such a characteristic curve represents the relation between an applied tuning voltage Vtune and an oscillation frequency. An exemplary oscillator circuit for a conventional voltage controlled oscillator is illustrated in The voltage controlled oscillator VCO further comprises a first tap point A If a supply voltage is now applied between the supply voltage terminal Vdd and the ground potential terminal Vss, the oscillator circuit VCO illustrated in As a further interpretation of the circuit illustrated in Furthermore, a current flow to the ground potential terminal Vss via the first transistor T The more linear a relation between an applied tuning voltage and an oscillator frequency, the more favourable are its properties, for example when used in a phase locked loop (PLL). Particularly a voltage controlled oscillator VCO with constant inductance, as the inductances L However, such a varactor element consisting of the auxiliary transistors T Such problems concerning the steep capacitance behaviour of the capacitance as a function of the tuning voltage also occur in other fields of application, such as measuring technology where a maximally linear behaviour of the individual electronic devices is desirable over the entire dynamic range of measuring devices. It is an object of the present invention to provide a circuit with variable capacitance and a method for operating a circuit with variable capacitance which allow a variable capacitance so that a more linear and flatter characteristic tuning curve may be provided as compared to a characteristic tuning curve of a conventional circuit. Further, it is an object of the present invention to provide a way to make a steepness of the characteristic tuning curve of the circuit variable. Further, it is the object of the present invention to provide an oscillator circuit and a method for operating an oscillator circuit, so that a variable adjustability of an output frequency of the oscillator circuit is made possible, and/or so that a more linear and flatter characteristic tuning curve of an oscillator circuit is provided as compared to a characteristic tuning curve of a conventional oscillator circuit. Further, it is an object of the present invention to provide a way to make a steepness of the characteristic tuning curve of the oscillator circuit variable. Further, it is an object of the present invention to be able to provide the more linear and flatter characteristic tuning curve in a simple and cost-efficient way. In accordance with a first aspect, the present invention provides a circuit with variable capacitance having: a capacitance, wherein the capacitance includes a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance; and a unit for providing the first bias and the second bias. In accordance with a second aspect, the present invention provides a method for operating a circuit with variable capacitance, wherein the circuit with variable capacitance includes a capacitance having a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, and a unit for providing the first bias and the second bias, the method having the steps of: providing the first bias and the second bias; and tapping off a voltage dropping at the capacitance of the circuit with variable capacitance to output the same as output signal of the circuit with variable capacitance. In accordance with a third aspect, the present invention provides a computer program with program code for performing the above-mentioned method, when the program runs on a computer. In accordance with a fourth aspect, the present invention provides an oscillator circuit having an inductance; a capacitance connectable in series to the inductance, wherein the capacitance includes a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance; and a unit for providing the first bias and the second bias. In accordance with a fifth aspect, the present invention provides a method for operating an oscillator circuit, wherein the oscillator circuit includes an inductance, a capacitance connectable in series to the inductance, the capacitance having a first partial capacitance and a second partial capacitance connected in parallel to the first partial capacitance, wherein a capacitance value of the first partial capacitance depends on a first bias of the first partial capacitance, and a capacitance value of the second partial capacitance depends on a second bias of the second partial capacitance, and a unit for providing the first bias and the second bias, the method having the steps of providing the first bias and the second bias; tapping off a voltage dropping at the capacitance of the oscillator circuit to output the same as output signal of the oscillator circuit. In accordance with a sixth aspect, the present invention provides a computer program with program code for performing the above-mentioned method, when the program runs on a computer. The present invention is based on the finding that connecting in parallel a first partial capacitance whose capacitance value depends on a first bias with a second partial capacitance whose capacitance value depends on a second bias creates the possibility to achieve a continuous extension of the characteristic tuning curve without complex switching. This is particularly because the selection of the first bias with respect to the second bias may preferably be performed such that the first bias differs from the second bias. By connecting the first partial capacitance and the second partial capacitance in parallel, an overlapping of the transition areas of the capacitance characteristic of the first partial capacitance with the capacitance characteristic of the second partial capacitance is achieved. If different biases are used between the used partial capacitances, there is an offset of the transition areas of their capacitance characteristics of the individual partial capacitances, resulting in flattening the capacitance behaviour of the total capacitance. This results in avoiding the switching of various characteristic tuning curves to achieve an extension and flattening of the characteristic tuning curves. Preferably, the first partial capacitance may include two auxiliary capacitances connected in series with a first tap point in-between, and the second partial capacitance may include two further auxiliary capacitances connected in series with a second tap point in-between, wherein the first bias is defined by a potential difference between the first tap point and a ground potential terminal, and the second bias is defined by a potential difference between the second tap point and the ground potential terminal. With such a design of the first partial capacitance and the second partial capacitance, the first partial capacitance may thus be biased with a first bias, and the second partial capacitance may be biased with a second bias in a simple way. If, for example, the first tap point and the second tap point are connected to each other via an ohmic resistor, and the first tap point is electrically connected to a support voltage terminal, and the second tap point is connected to a potential corresponding to the potential of the ground potential terminal, this results simply in a first bias at the first tap point differing from the second bias at the second tap point. If the auxiliary capacitances are preferably designed as MOS transistors, analogously to the conventional method, and if, for example, a tuning voltage is applied to the partial capacitances, the capacitance characteristic of the partial capacitances has a steeper curve in a defined tuning voltage interval. Outside this tuning voltage interval, the partial capacitances then, for example, assume saturation values and are nearly independent of the tuning voltage in such areas of the tuning voltage. Due to the fact that now the biases of the individual partial capacitances are “offset” with respect to each other, a total capacitance of the electronic circuit may thus be constructed, by the overlay and the shift as well as the parallel connection of the individual partial capacitances, which has a longer and flatter capacitance value characteristic as compared to the capacitance characteristic of the individual partial capacitances. The present invention thus offers the advantage to avoid a complicated and thus cost-intensive switching between individual characteristic tuning curves by a simple circuit engineering measure. The result of the resulting overlay is a significantly flatter and more linear characteristic capacitance curve than is the case for a conventional characteristic capacitance curve. Furthermore, it is, for example, possible to change a voltage difference between the first tap point and the second tap point by varying the current flow through an electric resistor connecting the first tap point to the second tap point. This is particularly because the voltage dropping at the ohmic resistor between the first tap point and the second tap point is proportional to the current flow through this ohmic resistor. Thus if, for example, the current flow through the ohmic resistor is increased or the resistance of the resistor is increased, the voltage difference between the first tap point and the second tap point also increases resulting, in turn, in an increase of the mutual offset of linear areas (i.e. the transition areas) of the individual partial capacitances. By a variation of the offset of the linear partial areas of the individual partial capacitances, it is thus possible to change the steepness of the characteristic tuning curve with respect to a variation of the tuning voltage. Such an electronic circuit thus offers the further advantage to provide, in a simple manner, a linearization of the characteristic tuning curve of the electronic circuit, in which the steepness of the characteristic tuning curve is also variable and in which switching between individual characteristic curves is avoided. This results in an improved characteristic of the electronic circuit and thus makes the inventive electronic circuit usable in a considerably broader field of application as compared to a corresponding conventional electronic circuit. Preferred embodiments of the present invention will be explained in the following with respect to the accompanying drawings, in which: In the following description of the preferred embodiments of the present invention, equal or similar reference numbers are used for elements illustrated in the various drawings and acting similarly, wherein a repeated description of these elements is omitted. Preferably, the individual auxiliary transistors of the partial capacitances each have a ratio of a channel width W/n to a channel length L which is reduced by the factor n compared to the conventionally used auxiliary transistors T The oscillator circuit illustrated in Furthermore, the first tap point AP Considering the design of the ohmic resistors R through which the respective tap points of partial capacitances are connected to the adjacent tap points of the adjacent partial capacitances, this results in a voltage difference ΔU, whereby the voltage U The current source With a thus designed current source With a thus stepped bias current I In order to obtain the characteristic curves illustrated in In order to operate the oscillator circuit described above, it is necessary, as compared to the conventional method, to provide a first bias and a second bias with which the first partial capacitance and the second partial capacitance may be provided. After that, the desired steepness of the characteristic tuning curve may be adjusted. When the oscillator circuit is settled, a voltage dropping at the total capacitance of the oscillator circuit may be tapped off to output the same as output signal of the oscillator circuit. However, the electronic circuit with variable capacitance in the form of individual partial capacitances shown in the example of the oscillator circuit may also be used for other fields of application. The only thing to be taken into account is that, by the connection of the individual partial capacitances, as set forth above, a total capacitance is achieved which allows a realization of a more linear and flatter characteristic curve of the capacitance of the electronic circuit. In summary it may thus be said, that switching to several characteristic tuning curves, as is necessary in conventional oscillator circuits, may be avoided when an extension of the active tuning area is performed by means of the inventive approach. For this, the varactor element used in conventional oscillator circuits (i.e. the partial capacitance used in a conventional oscillator circuit) is split into many individual varactors of equal size. These individual varactors, in turn, obtain their own DC bias points (i.e. tap points) in pairs, which differ stepwise by, for example, several hundred mV from each other. The number of pairs and the voltage difference between the bias points determine the length and linearity of the thus generated tuning curve. An example for a realization can be seen in This makes use of the fact that the DC difference voltage across the varactor determines its respective capacitance value. With the difference voltages being stepped, the individual varactor pairs are in different states. By changing the tuning voltage, the difference voltages are shifted all together by the same amount and the varactors pass from one state to the next one after the other. This is because the varactor has three state areas, either its maximum or minimum capacitance (saturation area) and, in-between, the relatively short transition area. By the biasing discussed above, these transition areas are offset against each other so that there is a mutual overlap. When a varactor has left its transition area, its capacitance value remains stable, and the next varactor is in this transition state. In this way, all varactors are successively transferred from the minimum capacitance value Cmin illustrated in In the example, the biasing is generated via a current source and, for example, a number of equal resistors R. An advantage of this is the matching behaviour in integrated circuits. However, the biasing may also be generated in any other way, the steps may also be selected as desired, and thus it would theoretically be possible to generate any desired characteristic curves. It further is to be noted that a conventional VCO generally has one or more characteristic tuning curves which have a determined steepness which determines the steepness of the circuit. In most cases, the steepness is abbreviated Kvco and has the unit Hz/V. If it is required to control this steepness in a defined way without changing the tuning area, the oscillator circuit described above is recommended. It is preferred to use varactor pairs (i.e. partial capacitances) with linearly stepped bias points, as illustrated in A voltage difference between adjacent bias points is ΔU. If this voltage difference is changed, the position of the individual characteristic curves with respect to each other and thus the length of the total characteristic tuning curve and thus also its steepness also change. With a larger ΔU, the characteristic curve becomes flatter, with a smaller ΔU, it becomes steeper up to the maximum steepness at ΔU=0 Volt. This connection is again illustrated in the This voltage difference is preferably formed at a resistor with the aid of the bias current I For the entire tuning area to be maintained, it should be ensured that all varactor pairs are completely switched when the tuning voltage Vtune passes through. The simulation result for such an oscillator circuit is illustrated in Depending on the circumstances, the inventive method for operating a circuit with variable capacitance may be implemented in hardware or in software. The implementation may be performed on a digital storage medium, particularly a floppy disc or CD with control signals that can be read out electronically, which may cooperate with a programmable computer system so that the corresponding method is carried out. Generally, the invention thus also consists in a computer program product with a program code stored on a machine-readable carrier for performing the inventive method, when the computer program product runs on a computer. In other words, the invention may thus be realized as a computer program with a program code for performing the method, when the computer program runs on a computer. While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention. Patent Citations
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